Biomedical subjects

S P Scalaidhe

Publications and source records attributed to S P Scalaidhe.

5 recordsLinked to original sources

PubMed1997

The effects of combined superior temporal polysensory area and frontal eye field lesions on eye movements in the macaque monkey.

We previously found [42] that lesions of the superior temporal polysensory area (STP) cause temporary deficits in the production of eye movements. In order to both define regions participating in the ensuing recovery and to further explore the cortical control of eye movements, we examined the effects of addition of frontal eye field (FEF) lesions to STP lesions, on visual fixation, saccadic eye movements, and smooth pursuit eye movements. Three monkeys received bilateral STP lesions followed by a FEF lesion and as a control, an additional monkey received a bilateral inferior temporal cortex (IT) lesion followed by a FEF lesion. All animals had a profound impairment in foveating the central fixation point. This impairment was completely eliminated by turning on a dim light in the testing chamber. Large neglect-like impairments in making saccades were only seen after combined STP and FEF lesions. Impairments in making smooth pursuit eye movements after combined lesions of STP and FEF were larger than those seen after STP lesions but within the range of deficits that have been reported after FEF lesions alone. The impairment of visual fixation in darkness and the lack of impairment under conditions of dim illumination appear to reflect a specific role for the FEF in spatial orientation in the absence of visual landmarks. The FEF also appears to play a more critical role than STP in smooth pursuit. By contrast, STP and the FEF appear to work cooperatively with respect to the production of saccades. We suggest that cortical oculomotor control can flow either through the midbrain or through the FEF and that the FEF pathway is specifically involved in tasks with a discontiguity between the stimuli and the behavioral response while the midbrain pathways are preferentially involved in more stimulus-driven eye movements.

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PubMed1995

Effects of superior temporal polysensory area lesions on eye movements in the macaque monkey.

1. On the basis of its anatomic connections and single-unit properties, the superior temporal polysensory area (STP) would seem to be primarily involved in visuospatial functions. We have examined the effects of lesions of STP on saccadic eye movements, visual fixation, and smooth pursuit eye movements to directly test the hypothesis that STP is involved in visuospatial and visuomotor behavior. 2. Seven monkeys were trained to make saccades to targets 8, 15, and 22 degrees from a central fixation point along the horizontal meridian and 8 degrees from the central fixation point along the vertical meridian. One monkey was also trained to make saccades to auditory targets. The same monkeys were trained to foveate a stationary central fixation point and to follow it with a smooth pursuit eye movement when it began moving 5, 13, or 20 degrees/s. Four monkeys received unilateral STP lesions, one received a bilateral STP lesion, and as a control, two received unilateral inferior temporal cortex (IT) lesions. After testing, three of the animals with unilateral STP lesions received an additional STP lesion in the hemisphere contralateral to the first lesion. Similarly, one animal with a unilateral IT lesion received an additional IT lesion in the hemisphere contralateral to the first lesion. 3. All monkeys with complete removal of STP showed a significant increase in saccade latency to the most peripheral contralateral target, and most also had increased saccade latencies to the other contralateral targets. Saccades directed to targets along the vertical meridian or toward targets in the hemifield ipsilateral to the lesion were not impaired by removal of STP. By contrast, IT lesions did not impair the monkeys' ability to make saccadic eye movements to visual stimuli at any location, showing that saccades to visually guided targets are not impaired nonspecifically by damage to visual cortex. 4. The deficit in making eye movements after STP lesions was specific to saccade latency, with little effect on the accuracy of saccades to visual targets. 5. In the one monkey trained to make saccades to auditory targets, removal of STP did not impair saccades to auditory targets contralateral to its lesion, despite this monkey showing the largest increase in saccades latencies to visual targets. 6. There was complete recovery of saccade latency to the baseline level of performance on the saccade task after all STP lesions.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1993

Dissociation of object and spatial processing domains in primate prefrontal cortex.

Areas and pathways subserving object and spatial vision are segregated in the visual system. Experiments show that the primate prefrontal cortex is similarly segregated into object and spatial domains. Neurons that code information related to stimulus identity are dissociable, both by function and region, from those that code information related to stimulus location. These findings indicate that the prefrontal cortex contains separate processing mechanisms for remembering "what" and "where" an object is.

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PubMed1993

Response properties of neurons in temporal cortical visual areas of infant monkeys.

1. Inferior temporal cortex (IT) is a "high-order" region of primate temporal visual cortex implicated in visual pattern perception and recognition. To gain some insight into the development of this area, we compared the properties of single neurons in IT in infant monkeys ranging from 5 wk to 7 mo of age with those of neurons in IT in adult animals. Both anesthetized and awake behaving paradigms were used. 2. In immobilized infant monkeys under nitrous oxide anesthesia, the incidence of visually responsive cells was markedly less than in adult monkeys studied under similar conditions. In infants 4-7 mo of age, only half of IT neurons studied were visually responsive, compared with > 80% in adult monkeys. In monkeys < 4 mo old, even fewer (< 10%) could be visually driven. "Habituation" of IT cells to repeated stimulus presentation appeared more pronounced in infant monkeys under nitrous oxide anesthesia than in adult animals. 3. IT cells in the anesthetized infant monkeys that did respond showed receptive field properties similar to those of responsive adult IT neurons studied under similar conditions. Two thirds of the receptive fields plotted in the anesthetized 4 to 7-mo-old group were bilateral, and median field size did not differ between the infants and comparable adult groups, being approximately 20 degrees on a side in each case. 4. In contrast to the results obtained under anesthesia, most IT cells in alert infant monkeys 5 wk-7 mo of age (80%) were responsive to visual stimuli, and this incidence of visually responsive IT neurons did not differ from that obtained in awake adult macaques. However, response magnitude, measured as spikes per second above baseline rate, was significantly lower in the infant alert sample than in the adult control (5.2 vs. 12.6 spikes/s, mean +/- SE, deviation from spontaneous rate, respectively). 5. In addition to having lower magnitudes of visual response, IT cells in the awake infants also tended to have longer and more variable latencies. The overall mean for the infant cells was 196 ms, compared with an overall mean of 140 ms for IT neurons in the alert control adult. 6. Although the magnitude of response of neurons in alert infant IT cortex was lower overall, the incidence and features of stimulus selectivity shown by alert infant IT neurons were strikingly similar to those of IT cells of both anesthetized and unanesthetized adult monkeys.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMedDate not supplied

Face-selective neurons during passive viewing and working memory performance of rhesus monkeys: evidence for intrinsic specialization of neuronal coding.

The functional organization of prefrontal cortex (PFC) is a central issue in cognitive neuroscience. Previous physiological investigations have often failed to reveal specialization within the PFC. However, these studies have generally not been designed to examine this issue. Methodological issues such as statistical criteria for specificity, the number of neurons sampled, the extent of cortex sampled, and the number, location and nature of the stimuli used are among the variables that need to be considered in evaluating the results of studies on functional localization. In the present study, we have examined neurons in macaque monkeys trained to fixate while viewing visual stimuli, including faces, or to use them as memoranda on a working memory task. Visual responses of over 1500 neurons were recorded throughout a wide expanse of the PFC (areas 12, 9, 46, 8 and 45). Neurons were considered selective for faces if the best response to a face was over twice as strong as that to any of a wide variety of non-face stimuli. Full electrode track reconstructions in three monkeys revealed in each that neurons which met this criterion were concentrated almost exclusively in three distinct subregions within the projection region of the temporal lobe visual areas. We further show that for all neurons, the most visually selective neurons (for faces, objects or color patterns) were also the most concentrated in the temporal lobe recipient PFC. Similar face selectivity, regional specialization, and delay or delay-like activity were observed in monkeys whether trained on memory tasks or not, which suggests that these are naturally occurring properties of prefrontal neurons. These results confirm neuronal and regional specialization for information processing in PFC and elucidate how heretofore unexamined experimental variables have a strong influence on the detection of regional specialization.

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